Question 334985
<pre><font size = 4><b> 
{{{system(a+b=15,
a+c=16,
b+c=11)}}}

Write it this way, so that all letters appear in all equations and
every letter has a coefficient showing:

{{{system(1a+1b+0c=15,
1a+0b+1c=16,
0a+1b+1c=11)}}}

On you TI-83 or TI-84,

Press ON
Press CLEAR

Press 2nd
Press x<sup>-1</sup>  (MATRIX)
Press right arrow key twice to highlight EDIT
Press 1
Press 3
Press ENTER
Press 4
Press ENTER

Press 1
Press ENTER
Press 1
Press ENTER
Press 0
Press ENTER
Press 15
Press ENTER
Press 1
Press ENTER
Press 0
Press ENTER
Press 1
Press ENTER
Press 16
Press ENTER
Press 0
Press ENTER
Press 1
Press ENTER
Press 1
Press ENTER
Press 11
Press ENTER

Press 2nd
Press MODE (QUIT)

Press 2nd
Press x<sup>-1</sup>  (MATRIX)
Press right arrow key to highlight MATH
Press ALPHA
Press APPS

You should see  rref(

Press 2nd
Press x<sup>-1</sup>  (MATRIX)
Press 1
Press ENTER

You should see 

rref([A]
    [[1 0 0 10]
     [0 1 0 5 ] 
     [0 0 1 6 ]]

The answers are a=10, b=5, c=6   

Edwin</pre>